Neurobiological mechanisms of nicotine reinforcement: Role of the nucleus tractus solitarius (NTS) Cigarette smoking is a principal cause of preventable death and disease in developed nations, with approximately $160 billion being spent yearly in the United States to cover direct health care costs from resulting diseases. Nicotine is the major psychoactive component of tobacco smoke responsible for tobacco addiction. Nicotine acts in the brain by stimulating nicotinic acetylcholine receptors (nAChRs), which are pentameric ion channels comprised of five discrete subunits. A major advance in our understanding of smoking behavior is the recent finding that genetic variation in the a3/ a5/4 nAChR subunit gene cluster on chromosome region 15q25 dramatically increases risk of tobacco addiction. Intriguingly, a3/ a5/4 nAChR subunits have a highly-restricted expression pattern in the brain, with the nucleus of the solitary tract (NTS) being one of the only brain regions to display robust expression of all three subunits. The NTS is involved in the regulation of feeding, respiration, processing of interoceptive information, and was recently implicated in opiate reward, yet its role in nicotine reinforcement remains largely unexplored. Preliminary data show that lidocaine-mediated NTS inactivation significantly reduces intravenous nicotine self-administration (IVSA) in rats. Furthermore, glucagon-like peptide-1 (GLP-1), a neuropeptide involved in regulating interoceptive stress and feeding inhibition, is produced in the NTS and represents one of its major efferent systems, projecting to brain regions related to drug reinforcement. Preliminary data show that GLP-1 neurons in the NTS are activated in response to acute nicotine injections. In addition, preliminary studies suggest that nicotine IVSA is almost completely abolished in mice lacking expression of the GLP-1 receptor. Taken together, these results suggest a regulatory role for the NTS, and perhaps GLP-1 transmission, in nicotine reinforcement. We aim to characterize the role of a3/ a5, and/or 4 -containing nAChRs in the NTS in nicotine reinforcement and how nAChRs containing these subunits may regulate NTS neurochemical systems such as GLP-1. To achieve this goal we propose to use an innovative mouse nicotine IVSA technique to test the effect of specific gene knockouts on volitional nicotine intake. In addition, we plan to employ cutting-edge viral- mediated gene transfer technologies to re-express or silence target genes in vivo, as well as immunochemical techniques for brain region-specific assessment of neuronal activation, and intracranial self-stimulation for direct inquiry of reward systems in rats and mice. Results from the experiments outlined in this proposal will increase our basic understanding of nicotine addiction, and may provide exciting targets for the development of novel therapeutics for smoking cessation.